Traditionally, a piloting device for piloting an aircraft comprises at least one piloting member connected, at least partially by a kinematic chain, to at least one flying member—in particular a control surface, an engine, etc.—of the aircraft, and possibly at least one motorised actuator, called a parallel actuator, having a driving member coupled in parallel in the kinematic chain so as to enable automatic piloting and/or to simulate a specific dynamic behaviour of the piloting member to bring about a return to neutral and create appropriate sensations (in particular muscular force sensations) enabling or facilitating the piloting by a human pilot.
The traditional, mechanically controlled, piloting devices comprise a kinematic chain connecting the piloting members to the flying members completely mechanically. Typically, the kinematic chain has a rod and/or articulation and/or slide linkage, enabling transmission of the displacement commands and the forces mechanically (possibly with amplification) between the piloting member and each flying member. Such piloting devices with completely mechanical control are still widely used in numerous aircrafts (small-size aeroplanes, helicopters, etc.).
Piloting devices with electrical flight controls, in which the flying members are not connected entirely mechanically by a kinematic chain to the piloting members have been developed for piloting certain aircrafts. These piloting devices with electrical flight controls have a partial kinematic chain comprising at least one mechanism for mounting and guiding each piloting member mounted and guided with respect to a frame integral with the aircraft, and having a set of position and/or force sensors connected to flight control computers generating control signals for a servo control with electrical input actuating one or more flying members.
In the particular case of a mini-stick for piloting aircraft, the piloting member is mounted and guided in rotation on two pivot joints with axes at least substantially orthogonal and intersecting (thus forming a centre-point rotary joint) making it possible to impart pitch and roll movements.
Such a piloting device generally comprises at least one force sensor measuring at least one component of the forces in the piloting device, by deformation of at least one deformable sensing element of the force sensor. Such a force sensor makes it possible, in particular, to carry out test flights, and supplies signals which are useful in the automatic actions associated with such piloting devices, for example for the coupling of a plurality of piloting members of the aircraft, and/or for delivering signals to an electronic device for operational control of the piloting device, and/or for the operation of the autopilot, and/or for control of motors associated with the degrees of freedom of the piloting member so as to achieve an electrically simulated variable force feedback sensation.
That being so, the aircraft piloting devices must be able to be subjected, for their certification, to maximum certification forces, the value of which is much higher than the nominal operational value of the forces during actual piloting of the aircraft. Typically, the value of the maximum certification forces is ten times greater than the nominal operational value. These certification forces are applied when the piloting member is placed in abutment with respect to the frame on one side or the other.
In order for the measurement of the forces to be as precise as possible, however, it is advisable to optimise the force sensor for the operational values of the forces applied in the piloting device, but not necessarily for the value of the certification forces. Thus, it must be possible to choose the force sensor so that it can have a measuring range covering the maximum operational value of the forces with a certain safety coefficient. In practice, the force sensor is chosen such that it can withstand 150% to 200% of the maximum operational value. In these conditions, it is advisable to avoid subjecting the force sensor directly to the value of the certification forces, which is liable to cause damage to or even destruction of the force sensor.
In certain known piloting devices (cf. for example JP 10059293) the force sensor is arranged in the kinematic chain downstream of the mechanism for mounting the piloting member, and the stops limiting the angular deflection of the piloting member are arranged between the force sensor and the piloting member. In these devices, the force sensor is isolated from the reaction forces when the piloting member is in abutment. This architecture nevertheless has the major disadvantage of not measuring the frictional forces developed in the mechanism for mounting and guiding the piloting member.
In other known piloting devices (cf. for example U.S. Pat. No. 8,050,780) the force sensor is arranged upstream of the mechanism for mounting the piloting member. With these known devices, the application of the certification forces requires a specific additional stop to be added in the region of the force sensor in order to avoid damage thereto. Such an assembly is, however, complex (therefore less reliable), bulky, heavy and costly.